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The paper reports a preliminary study of jets of active radicals used as igniters for lean mixtures. The jets were generated either by combustion or by electric discharge. Experiments were performed in a cylindrical steel vessel, 9 cm in diameter and 9 cm long, filled initially with either air or an ultra-lean (equivalence ratio: 0.5) methane-air mixture at atmospheric pressure and room temperature. Observations were made by schlieren photography, using a sub-microsecond spark discharge in air as a point light source. The gasdynamic properties of the jets were shown to be primarily governed by their initial velocity, while the particular process by which they were formed played, in this respect, a secondary role. The jets of radicals invariably appeared as turbulent plumes which were embedded in blast waves headed by hemispherical shock fronts.

The problem of knock is traced back to the earliest scientific paper on combustion in premixed gases written by Mallard and Le Chatelier. The pioneering contributions of Ricardo, Kettering and Semenov are then put in proper perspective. Upon the recognition of the fact that this phenomenon has been, and still is, imposing the major technological constraint upon the automotive and oil industries, its various cures are reviewed. Essential features of combustion instability leading to its onset are then exposed, and the methodology is outlined for a rational attack upon the problem it poses.

An experimental study of the induction period for ignition of fuel sprays with particular consideration of its dependence upon temperature and pressure is reported. Emphasis in the study was placed upon conditions of thermodynamically supercritical state for the fuel. The tests were performed in a stainless steel cylindrical chamber located in an oven, both provided with quartz windows for optical insight in axial direction of the radially injected spray. Spray formation and ignition were observed by high-speed schlieren cinematography concomitantly with measurements of chamber pressure and the displacement of the injector needle. The induction period was evaluated as the time interval between the rise in the displacement transducer signal and the instant when pressure attained three percent of its peak value.

Upon ‘harnessing the fire’ by the early pioneers, the quest for controlled combustion provided the major incentive for progress in engine technology. At first this involved primarily the problem of knock and later that of pollutant emissions. It appears that both can be solved by treating the engine cylinder not only as a source of power but also as a controllable chemical reactor. The principal concept whereby this can be accomplished involves multi-point ignition combined with charge dilution and stratification. Means for this purpose include jet ignition, product recirculation, and chemical additives. The most suitable for the realization of this concept is a direct injection two-stroke engine.

Formation of pulsed plasma jets, or puffs, was examined using several visualization techniques. Self-light streak photography was first employed to record salient global features of the development and structure of the jet. This provided information on the motion of the luminous gas particles in its core, revealing that plasma jets can have two distinct modes, being either totally subsonic or embodying a supersonic efflux manifested by the recorded streaks of Mach discs. At a fixed power pulse of electrical energy discharge in the plenum chamber, the outcome depends on the constriction imposed by an orifice at its outlet. Whereas the difference between the two types of jets was quite small, penetration in the subsonic case was found to be definitely larger than in supersonic.

The fact that, in our times, the execution of the exothermic process of combustion (‘heat release”) remains virtually uncontrolled is astonishing. Upon an attempt to rationalize this anomaly on historical grounds, technological means to rectify this astounding state of affairs are presented. They are based on the premise that, in the course of this process, the cylinder-piston enclosure is, in effect, a full-fledged chemical reactor. The salient feature of control is then active intervention into chemical reaction by turbulent jets. Principal elements of the control system are, as in any feedback mechanism, (1) sensors, (2) actuators and (3) a governor. The object of the first is to measure the profile of pressure - the useful output of the process. The second consists of a set of turbulent jet generators for injection of fuel and its mixing with air, as well as for ignition.